As stated by velias, you don't really need the extra VRAM, it does help if you are adding texture packs, maxing out the settings. However, for approximately $50-80 more, you could just buy a GTX 680 over a 4 GB 670. I also used to run crossfire and understand the frustration with it, now I'm happy with my HD 7970, great card, plays nice with Photoshop CS6.

There is no benefit unless you're doing 5760x1080/1200 with lots of anti aliasing. This depends on the 3d application of course.

If you're a single screen user there is absolutely no reason to get 4gb, even up to 2560x1600. 2gb is plenty, there are no games with assets exceeding 2GB unless you do something stupid like 8x SGSSAA. (anti aliasing is the #1 contributor to VRAM use). So thats why usually you can get away with FXAA or no AA at 5760x1200, 2gb will limit you to that while 4gb will let you do 4x MSAA or something higher. (again -- this depends on application. Some games will let you do 2X msaa and others will run out of VRAM at 5760x1200 unless you do FXAA) Anyway, the point is you don't need 4GB since you're doing 2560x1600.

Its a tragedy that many people don't understand how VRAM works and how anti aliasing contributes to most VRAM use in modern games. (this isn't directed at you btw ;) I see people suggesting 4GB for 1080p and it really is quite stupid.

Well said and mirrors my own thoughts and experiences. Unless you plan to do 3 monitor gaming going with the extra 2GB per card is a waste seeing as 95% of the games you play won't use up the entire 2GB on the standard 670.